1867C - Salyg1n and the MEX Game - CodeForces Solution

#include <bits/stdc++.h>
#define ll long long
using namespace std;

void reem()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
}

int a[100020];
void solve()
{
    int n,i,x,y=0;
    cin>>n;
    x=n;
    for ( i = 0; i <n ; ++i)
    {
        cin>>a[i];
        if(a[i]!=i)x=min(x,i);
    }
    while (y!=-1)
    {
        cout<<x<<endl;
        cin>>y;
        x=y;
    }

}


int main()
{
    reem();
    int t;
    cin >> t;
    while (t--)
    {
        solve();
    }
    return 0;
}